Equivalent Flange Pressure Method

[fred181]

I understand the equivalent pressure method to be a conservative method for evaluating tendency of a pipe flange to leak, and particularly when using the temperature/pressure ratings lookup as the threshold.

That said, for a scenario in which I have a class 250 flanged valve mated with a class 300 pipe flange, is it appropriate to use the Class 250 pressure/temperature ratings using this method? This sets the allowable flange pressure much lower than class 300, despite being the same size.

Thanks

 

[LittleInch]

ASME class 250 is for cast iron flanges.

They will be substantially lower than pressure /temperature rating than a class 300 which is a steel flange. You always rate to the lowest flange rating.

I'm not sure what an equivalent pressure method is tbh. Can you define this?

If your class 250 flange is indeed cast iron, make sure that your mating flange if it is steel is a FF Flat face or has the raised face machined off it otherwise you could very easily break your cast iron flange.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TBP]

I found this link for Crane valves, and I suspect all manufacture's will have the same ratings. You should - of course - verify this for yourself, for whatever make of valve you have/

ttps://cranecpe.com/wp-content/uploads/CP_EG-CR-CT-EN-L16-03-2013-12CV-302-CraneIron.pdf

The table on page 5 shows that for up to 12", their 250 CI valves are rated for 250 PSIG at 450*F.

250 cast iron flanges have a 1/16" raised face, while the Class 150's have a flat face. You should machine the raised face off any mating Class 150 steel flange, and use a full-face gasket.

 

[LittleInch]

Forgot to say the design code is ASME B 16.1 for class 250 flanges.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[FacEngrPE]

I have had good results calculating required gasket preload out of the Garlock Gasket Calculator..

The Gasket Calculator will work with any gasket suppliers material, except spiral gaskets, which will not work with flat faced flanges.

If you want no leaks, make sure the flanges are parallel.

 

[StressGuy]

You will want to use the lower pressure rating of the class 250 flanges as the others have noted. It is a conservative approach, but it does make for a good screening tool - i.e. if you pass this test then you should have no worries. Whereas failing the equivalent pressure check just means you need to look into a more rigorous analysis approach to determine if you have a problem with your bending loads.

Caesar actually has this capability built in and can check it for you at nodes where you designate it.

Edward L. Klein
Pipe Stress Engineer
Houston, Texas

"All the world is a Spring"

All opinions expressed here are my own and not my company's.